Forming a metal oxide film onto a substrate such as glass, a polymer or a semiconductor by sputtering or vacuum evaporation has been carried out in the past. In recent years, for reasons of reducing deposition costs and manufacturing large-scale products, there has been a trend towards increasingly larger areas which can be formed at one time. There has also been a steadily growing trend towards using resin substrates (for example, use of polycarbonate or acrylic) in place of glass as a substrate. With this move towards deposition of larger deposited film surface areas and non-heat resistant substrates, deposition that does not require heating is being widely carried out because deposition technologies that do heat the substrate cause the film to crack or damage the substrate.
However, in such a non-heating process, driving force and mobility for crystallization of the metal oxide is not supplied sufficiently. This means that the obtained film tends to be amorphous, making it difficult to achieve sufficient crystallinity. For that reason, in a case where a surface crystallinity greatly effects the characteristics of a product, it has been necessary to strictly control process conditions such as gas introduction. However, if such strict control of process conditions is required, it is often the case that the obtained film characteristics are inferior to those of films which were produced by a process which involves heat treatment of the substrate, even when it was thought that the process was comparatively successful.
One approach to reduce the extent of heating the substrate that has been widely used is to prepare an oxide film using a precursor solution containing an ion which comprises a metal element. Such a precursor solution includes a metal alkoxide, metal acetate, organic-metal complex, metal salt, metal soap and the like. A typical deposition method that uses these substances is a sol-gel method which uses a metal alkoxide solution. These deposition methods use water and a catalyst such as an acid for a solution containing an ion which comprises a metal element, wherein the ion comprising a metal element is made to transit from a low molecular state to a high molecular state, which is disorderly but has the molecules bonding to each other (this state is called gelation). At this stage heat is applied to remove organic substances at a comparatively low temperature, whereby a metal oxide can be obtained. Because this method has low equipment costs, and through dip coating or the like allows uniform deposition over an entire substance even for objects having an intricate shape, it is suitable for coating of thin film oxides for high-mix low-volume production or comparatively small objects. However, such a method has the drawback that it can only be applied to heat resistant substrates, because generally heat treatment of at least 400° C. is required for the combustion of organic material contained in the source solution, dehydration polycondensation inside the film or to promote crystallization.
Methods such as ultraviolet irradiation, steaming and electron beam irradiation are being investigated for these sol-gel process films as a technique for accelerating crystallization and densification without requiring heat treatment. Recently, Rengakuji of Toyama University (Japan) has reported that the addition of an aromatic compound such as benzene to a metal alkoxide allows the molecules in the alkoxide to be sandwiched by the benzene, and that a structure advantageous to crystallization can be formed by depositing it so as to make crystallization at a low temperature more easily carried out. However, this process also requires strict control process conditions similar to those mentioned above for the non-heat treatment processes. There are disadvantages such as insufficient repeatability and insufficient crystallization.
In view of the background described above, a technique for forming an amorphous metal oxide film on a substrate with low heat resistance such as a resin material and effectively crystallizing the film without deteriorating the substrate was extremely limited. In particular, there was almost no technique for sufficiently crystallizing an amorphous film simultaneously and uniformly over an entire object in a short period of time.
Highly advanced techniques for thin films using plasma which pertains to the present invention include Japanese Patent Laid-Open No. 4-149090, U.S. Pat. No. 6,432,725, Japanese Patent Laid-Open No. 07-294861, Japanese Patent Laid-Open No. 04-199828, Japanese Patent Laid-Open No. 2001-148377, Japanese Patent Laid-Open No. 2001-31681, Japanese Patent Laid-Open No. 2001-133466, Japanese Patent Laid-Open No. 09-64307, Japanese Patent Laid-Open No. 10-233489, Japanese Patent Laid-Open No. 2000-200899, Japanese Patent Laid-Open No. 09-153491, Japanese Patent Laid-Open No. 09-246477, Japanese Patent Laid-Open No. 2001-152339, Japanese Patent Laid-Open No. 10-273317, Japanese Patent Laid-Open No. 09-262466, Japanese Patent Laid-Open No. 2001-85639, Japanese Patent Laid-Open No. 2000-86242, Japanese Patent Laid-Open No. 02-283022 and Japanese Patent Laid-Open No. 11-145148. The main differences between what is disclosed in these techniques and the present invention will be described below.